A coil (also referred to as an inductor) is an electronic component. This component may be implemented using an electrical conductor wound one or more times to form a shape of a coil, a spiral, or a helix. As such, when an electric current flows through the windings, the coil may have an inductance value. The inductance value for a coil of wire may be approximated by the following equation:
  L  =                    N        2            ⁢      μ      ⁢                          ⁢      A        I  
where                L is the inductance of the coil in henries (H);        N is the number of turns in the wire coil (for example, a loop of wire has an N equal to 1);        μ=μrμ0 is the permeability of the core material or medium;        μr is the relative permeability of the core material or medium relative to the permeability of a vacuum;        μ0 is the permeability of the vacuum (approximately 4π(10−7) H/m, where m is meter);        A (m2) is the average area of the core; and        l is the average length of the coil wiring in meters.        
Some inductors may be tunable, and these tunable inductors can be used for tunable filtering, tunable matching, tunable harmonic suppression, tunable oscillators, and the like. Some surface mount device (SMD) tunable coils rely on a mechanical screw to tune the coil. When this is the case, mechanical tuning is commonly performed only once during the assembly, and once tuned, the mechanical tuning may not be easily changed afterwards.